Air seal interface with AFT engagement features and active clearance control for a gas turbine engine

ABSTRACT

An interface for a gas turbine engine. The interface includes a full-hoop vane ring around the engine axis, the full-hoop vane ring comprises a forward vane rail with a vane ring forward contact surface and a vane ring anti-rotation tab, the vane ring anti-rotation tab engaged with the anti-rotation case slot; and a multiple of BOAS segments around the engine axis, each of the multiple of BOAS segments comprise a BOAS aft engagement feature and a BOAS aft contact surface, the BOAS aft engagement feature engaged with the outer case and the anti-rotation case slot, the BOAS aft contact surface abuts the vane ring forward contact surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/194,857 filed Nov. 19, 2018.

U.S. GOVERNMENT RIGHTS

This invention was made with Government support under contractW58RGZ-16-C-0046 awarded by the United States Army. The Government hascertain rights in the invention.

BACKGROUND

The present disclosure relates generally to a gas turbine engine, andmore particularly to an air seal interface arrangement.

Gas turbine engines include a compressor that compresses air, acombustor that burns the compressed air, and a turbine across which thecombustion gases are expanded. The expansion of the combustion gasesdrives the turbine, which in turn drives rotation of a power turbine andthe compressor.

Turboshaft engines, which are often used in rotary wing aircraftapplications, are typically smaller than turbofan aircraft engines andare often subject to prolonged operations in dusty environments. Thesefactors often require an erosion resistant abradable blade outer airseal in the compressor. The relatively small engine diameter makesefficiency and stability sensitive to tip clearance, while the harshoperating environment tends to erode the abradable coatings atundesirable rates.

An engine casing of an engine static structure may include one or moreblade outer air seals (BOAS) that provide an outer radial flow pathboundary for the hot combustion gases. The BOAS surround respectiverotor assemblies that rotate and extract energy from the hot combustiongases. The BOAS may be subjected to relatively intense temperaturesduring gas turbine engine operation.

In order to increase efficiency, a clearance between the blade tips ofthe rotor assemblies and the outer radial flow path boundary isrelatively small. This ensures that a minimum amount of air passesbetween the blade tips and the outer radial flow path boundary. Theabradable BOAS further reduces the tip clearance as the blade tips aredesigned to, at times, rub against the BOAS. The rubbing wears theabradable material such that the blade tips then have a reduced tipclearance relative to the idealized geometry.

The performance impact of leakage at the blade tip is proportional tothe ratio between the tip clearance (gap between the blade tip shroudand BOAS), and the overall size of the flow path such that, the smallerthe engine the larger the percentage that the tip clearance is relativeto the whole flow. Relatively small engines are thus much more sensitiveto tip clearance than larger engines. The lowest leakage design is afull-hoop BOAS ring because it eliminates the additional leakage due tothe gap between adjacent segmented BOAS. However, a full-hoop BOAS ringcomplicates design of a tight tip clearance in a power turbine becausethe BOAS ring typically grows more in radius than do the rotor bladeswhich increases the tip clearance.

Power turbines may be particularly difficult to seal due to the size ofengine components and the relative tolerances. As a result, it isadvantageous to design full-hoop ring blade outer air seals and vanes.The nature of the full-hoop design has very low inherent leakage, duethe absence of segmentation gaps. However, the nature of full-hoop ringresults in more significant thermal expansion and contractionindependent of the surrounding engine case structures, which precludesthe use of active clearance control systems. Active clearance controlsystems shrink the outer engine case with cool air, which movessegmented vanes and BOAS inward to reduce tip clearance.

SUMMARY

An interface for a gas turbine engine according to one disclosednon-limiting embodiment of the present disclosure includes an outer casethat defines an engine axis, the outer case comprises an anti-rotationcase slot; a full-hoop vane ring around the engine axis, the full-hoopvane ring comprises a forward vane rail with a vane ring forward contactsurface and a vane ring anti-rotation tab, the vane ring anti-rotationtab engaged with the anti-rotation case slot; and a multiple of BOASsegments around the engine axis, each of the multiple of BOAS segmentscomprise a BOAS aft engagement feature and a BOAS aft contact surface,the BOAS aft engagement feature engaged with the outer case and theanti-rotation case slot, the BOAS aft contact surface abuts the vanering forward contact surface.

A further embodiment of any of the foregoing embodiments include thatthe vane ring forward contact surface loads against the BOAS segmentcontact surface in response to attachment of a second outer case to theengine case, the second case abuts with the full-hoop vane ring.

A further embodiment of any of the foregoing embodiments include thatthe second case module comprises a turbine exhaust case.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes a full hoop seal arranged around the engine axis,the multiple of BOAS segments load against the full hoop seal.

A further embodiment of any of the foregoing embodiments include thatthe full hoop seal is a dogbone seal.

A further embodiment of any of the foregoing embodiments include thatthe BOAS aft engagement feature of each of the multiple of BOAS segmentscomprises at least one BOAS anti-rotation tab.

A further embodiment of any of the foregoing embodiments include thatthe BOAS aft engagement feature is engaged with the engine case, theBOAS aft engagement feature forms a forward facing hook.

A further embodiment of any of the foregoing embodiments include thatthe BOAS anti-rotation tab abuts the vane ring anti-rotation tab.

A further embodiment of any of the foregoing embodiments include thatthe forward vane rail comprises a groove to receive a seal.

A further embodiment of any of the foregoing embodiments include thateach of the multiple of BOAS segments comprises a circumferentialfeather seal slot to seal between each of the multiple of BOAS segments.

A further embodiment of any of the foregoing embodiments include thatthe BOAS segment contact surface is transverse to the BOAS aftengagement feature.

A further embodiment of any of the foregoing embodiments include thatthe outer case comprises a case groove with an anti-rotation slot thatreceives the vane ring anti-rotation tab and the BOAS anti-rotation tab.

A further embodiment of any of the foregoing embodiments include thatthe BOAS aft engagement feature comprises a rail with the BOASanti-rotation tab to receive the vane ring anti-rotation tab.

A further embodiment of any of the foregoing embodiments include thatthe wherein the BOAS aft engagement feature is a hooked rail.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes a BOAS forward engagement feature received within agroove in the case, the BOAS aft engagement feature forms a hook.

A further embodiment of any of the foregoing embodiments include thatthe hooked rail extends forward engagement feature.

A method of assembling a module for a gas turbine engine according toone disclosed non-limiting embodiment of the present disclosure includesinstalling a full-hoop vane ring around an engine axis into a casegroove with an anti-rotation slot in an engine case, the full-hoop vanering comprises an aft vane rail with a vane ring forward contact surfaceand a vane ring anti-rotation tab received into the anti-rotation slotin an engine case; and installing a multiple of BOAS segments around theengine axis, each of the multiple of BOAS segments comprise a BOAS aftengagement feature, a BOAS aft contact surface, and a BOAS anti-rotationtab, the BOAS anti-rotation tab engaged with the anti-rotation case slotsuch that the BOAS aft contact surface abuts the vane ring forwardcontact surface.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes attaching a second outer case to seal the BOASsegment contact surface with the vane ring forward contact surface.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes compressing a seal between the full-hoop vane ringand a second multiple of BOAS segments forward of the full-hoop vanering.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes installing the seal within a groove formed in thefull-hoop vane ring.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be appreciated that the following description anddrawings are intended to be exemplary in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example turboshaft gas turbine engine.

FIG. 2 is a schematic block diagram view of a stage in a section of thegas turbine engine.

FIG. 3 is a schematic view of an example air seal interface arrangementin a power turbine module section of the gas turbine engine.

FIG. 4 is an exploded view of the air seal interface arrangement betweenone blade outer air seal segment, a full hoop vane ring, and an enginecase within the power turbine module section of the gas turbine engine.

FIG. 5 is a cross-sectional view taken along line 4-4 in FIG. 4 of theFIG. 4 air seal interface arrangement in an assembled condition.

FIG. 6 is a cross-sectional view of an alternative embodiment of the airseal interface arrangement with a W seal at a aft interface of the bladeouter air seal segment.

FIG. 7 is a cross-sectional view of an alternative embodiment of the airseal interface arrangement with a diamond seal at a aft interface of theblade outer air seal segment.

FIG. 8 is an exploded view of an alternative embodiment of the air sealinterface arrangement.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 10. In thisembodiment, the engine 10 is a three-spool turboshaft engine, such asfor a helicopter with a low spool 12, a high spool 14 and a powerturbine spool 33 mounted for rotation about an engine centrallongitudinal axis A. The engine 10 includes an inlet duct module 22, acompressor section 24, a combustor section 26, a turbine module 28, anda power turbine module 34.

The compressor section 24 includes a low pressure compressor 42 with amultitude of circumferentially-spaced blades 42 a and a centrifugal highpressure compressor 44 a multitude of circumferentially-spaced blades 44a. The turbine section 28 includes a high pressure turbine 46 with amultitude of circumferentially-spaced turbine blades 46 a and a lowpressure turbine 48 with a multitude of circumferentially-spaced blades48 a. The low spool 12 includes an inner shaft 30 that interconnects thelow pressure compressor 42 and the low pressure turbine 48. The highspool 14 includes an outer shaft 31 that interconnects the high pressurecompressor 44 and the high pressure turbine 46.

The low spool 12 and the high spool 14 are mounted for rotation aboutthe engine central longitudinal axis A relative to engine staticstructure modules 22, 27, and 29 via several bearing systems 35. Thepower turbine spool 33 is mounted for rotation about the engine centrallongitudinal axis A, relative to the engine static structure modules 22,27, and 29 via several bearing systems 37. The engine static structuremodules 22, 27, and 29 may include various static structure such as amid-turbine frame, a power turbine case, a turbine exhaust case andother structures. It should be appreciated that additional oralternative modules might be utilized to form the outer case assembly.

The compressor section 24 and the turbine section 28 drive the powerturbine section 34 that drives an output shaft 36. In this exampleengine, the compressor section 24 has five stages, the turbine section28 has two stages and the power turbine section 34 has three stages.During operation, the compressor section 24 draws air through the inletduct module 22. In this example, the inlet duct module 22 opens radiallyrelative to the central longitudinal axis A. The compressor section 24compresses the air, and the compressed air is then mixed with fuel andburned in the combustor section 26 to form a high pressure, hot gasstream. The hot gas stream is expanded in the turbine section 28 and thepower turbine section 34, which rotationally drives the compressorsection 24. The hot gas stream exiting the turbine section 28 furtherexpands and drives the power turbine section 34 and the output shaft 36.The compressor section 24, the combustor section 26, and the turbinesection 28 are often referred to as the gas generator, while the powerturbine section 34 and the output shaft 36 are referred to as the powersection. Although not shown, the main shaft 30 may also drive agenerator or other accessories through an accessory gearbox. The gasgenerator creates the hot expanding gases to drive the power section.Depending on the design, the engine accessories may be driven either bythe gas generator or by the power section. Typically, the gas generatorand power section are mechanically separate such that each rotate atdifferent speeds appropriate for the conditions, referred to as a ‘freepower turbine.’

FIG. 2 illustrates a stage of an engine section 40 of the gas turbineengine 20 of FIG. 1. In the disclosed illustrated embodiment, the enginesection 40 represents the power turbine module 34 (FIG. 1), however,other engine sections and architectures will benefit herefrom. Theengine section 40 contains a multiple of full hoop vane rings 56 and amultiple of blade outer air seal (BOAS) assemblies 70 supported withinthe case 52. The disclosed power turbine 34 includes two vane rings 54and three blade outer air seal (BOAS) assemblies 70 (FIGS. 3 and 4). Thetwo vane rings 54 and three blade outer air seal (BOAS) assemblies 70define a stack 110 that is assembled into the case 52.

Each full hoop vane ring 54 contains a multiple of vanes 56 that preparethe airflow for the blades 50. Each blade outer air seal (BOAS) assembly70 includes a multiple of blade outer air seal (BOAS) segments 72. EachBOAS segment 72 of this exemplary embodiment is circumferentiallydisposed about the engine centerline longitudinal axis A and is hookedinto the engine case 52. Each of the multiple of BOAS segments 72include a circumferential feather seal slot 71 to receive a feather sealbetween each of the multiple of BOAS segments 72. The ring of bladeouter air seal (BOAS) segments 72 establishes an outer radial flow pathboundary of the core flow path. The multiple of blade outer air seal(BOAS) segments 72 permit movement in response to the thermal expansionand contraction of the case 52.

Each BOAS segment 72 is disposed in an annulus radially between the case52 and the blade tip 58. The blade outer air seal (BOAS) assembly 70circumscribes associated blades 50 in the stage. Each blade of themultiple of blades 50 include a blade tip 58 with a knife edge 60 thatextends toward the respective blade outer air seal (BOAS) assembly 70.The knife edge 60 and the ring of blade outer air seal (BOAS) segments72 cooperate to limit airflow leakage around the blade tip 58.

Each BOAS segment 72 includes a BOAS body 80 having a radially innerface and a radially outer face. The radially inner face is directedtoward the blade tip 58 and the radially outer face faces the case 52.Each BOAS segment 72 may be manufactured of a material having arelatively low coefficient of thermal expansion such as anickel-chromium-iron-molybdenum alloy or other material that possesses adesired combination of oxidation resistance, fabricability andhigh-temperature strength. Example materials include, but are notlimited to, Mar-M-247, Hastaloy N, Hayes 242, IN792+Hf, HASTELLOY Xalloy (UNS N06002 (W86002). Other materials may also be utilized. One ormore cooling fins 96 may circumscribe the radially outer face of theBOAS body 80. An abradable seal 98 (also shown in FIG. 4) is secured tothe radially inner face of the BOAS body 80. In one example, theabradable seal 98 is a honeycomb seal that interacts with the blade tip58. A thermal barrier coating may partially or completely fill the seal98 to protect the underlying BOAS body 80 from exposure to hot gas,reducing thermal fatigue and to enable higher operating conditions.

With reference to FIG. 3, the power turbine section 34 of the gasturbine engine 20 in this embodiment includes a stacked arrangement ofblade outer air seal (BOAS) assemblies 70 (three shown) that areinstalled into the outer case 52, adjacent, and mechanically coupled to,the full-hoop vane rings 54 (two shown) that are also installed to theouter case 52 to form an air seal interface arrangement 114 for thestack 110. The stack 110 is axially clamped, thus the axial clamp load,in combination with the axial gas load, compresses the stacked bladeouter air seal (BOAS) assemblies 70 and vane rings 54 to form a stableair seal interface arrangement 114 between the stack 110 and the case52. A seal member 62, e.g., a dogbone seal, accommodates compression ofthe stack 110 in response to axial assembly of the static structuremodules.

With reference to FIG. 4, the outer case 52 is defined around the engineaxis A and includes a case groove 130 with at least one anti-rotationvane slot 132. Although only a single BOAS segment 72 will be describedin detail, each BOAS segment 72 installation is generally equivalent andeach stage in the power turbine section is generally similar as wellsuch that only one need be specifically described.

The full-hoop vane ring 54 includes an aft vane rail 140 with a vanering forward contact surface 142. The aft vane rail 140 is engaged withthe outer case 52 with a vane ring anti-rotation tab 144. The full-hoopvane ring 54 can thermally expand and contract radially independentlywith respect to the engine case 52 but is rotationally fixed againsttorque loads.

An active clearance control system 74 (illustrated schematically)permits changes in the diameter of the blade outer air seal (BOAS)assembly 70 but does not affect the full hoop vane ring 54.

Each BOAS segment 72 includes outer case attachment features such asforward engagement features 120 and an BOAS aft engagement features 122(that face engine front) that engage corresponding case engagementfeatures 121, 123 (FIG. 3; that face engine aft) that extend radiallyinwardly from the outer case 52 to provide thermal growth independence,while maintaining the radial fixity requirements of the BOAS segment 72.In this example, the BOAS aft engagement features 122 forms a forwardfacing hook.

The forward engagement features 120 includes a BOAS contact surface 150that loads against the corresponding vane ring forward contact surface142 and a BOAS aft engagement feature 122 that engages the case groove130. The BOAS aft engagement feature 122 includes a BOAS anti-rotationtab 153 that engages the vane ring anti-rotation tab 144 (FIG. 5). Thevane ring anti-rotation tab 144 abuts the BOAS anti-rotation tab 153which are then locked within the anti-rotation case slot 132 and theforward vane ring rail contact surface 148 abuts the BOAS aft contactsurface 160 of the BOAS aft engagement features 122.

The contact surfaces 148, 160 provide a facial axial interface (FIG. 5).Each stage in the stack 110 utilizes such an interface to create stableseal therebetween. In this embodiment, the engine static structure 29(FIG. 3) such as a turbine exhaust case is assembled to the powerturbine case 52 to compress the stack 110 at the BOAS aft contactsurface 160 on the aft most BOAS segment 72. That is, the power turbinecase 52 is assembled between the engine static structures 27, 29, e.g.,the mid turbine frame case and the turbine exhaust case.

With reference to FIG. 6, in embodiments, a W-seal 180 (FIG. 6), or adiamond seal 190 (FIG. 7) may be located in a cavity 182 in the forwardvane rail 146 to further minimize air leakage between the BOAS aftengagement features 122 and the forward vane rail 146 of the stack 110.The example W-seal 180 and diamond seal 190 may be manufactured of aprecipitation hardened formable superalloy singe crystal composition.

With reference to FIG. 8, another embodiment of the interface includes aseparate BOAS anti-rotation tab 153A that engages a separate slot 132Ain the case 52. The usage of separate slots facilities a differentquantity of vane ring anti-rotation tab 144 compared to BOASanti-rotation tab 153A. For example, 8-12 vane ring anti-rotation tab144; and 6-20 BOAS anti-rotation tab 153A.

Retaining the full hoop vane rings avoids segmentation leaks in theregions of high flow velocity (and lo static pressure) in the vanethroat. The vane rings can be cast as one-piece components. The fullhoop vane rings in conjunction with a segmented BOAS assembly enablesthe use of active clearance control to gain performance.

The architecture facilitates control of the segmented BOAS assembly viaan active cooling system, thus increasing engine power and low rpmefficiency.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the figures or all ofthe portions schematically shown in the figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The elements described and depicted herein, including in flow charts andblock diagrams throughout the figures may show logical boundariesbetween the elements. However, according to software or hardwareengineering practices, the depicted elements and the functions thereofmay be implemented on machines through computer executable media havinga processor capable of executing program instructions stored thereon asa monolithic software structure, as standalone software modules, or asmodules that employ external routines, code, services, and so forth, orany combination of these, and all such implementations may be within thescope of the present disclosure.

The use of the terms “a”, “an”, “the”, and similar references in thecontext of description (especially in the context of the followingclaims) are to be construed to cover both the singular and the plural,unless otherwise indicated herein or specifically contradicted bycontext. The modifier “about” used in connection with a quantity isinclusive of the stated value and has the meaning dictated by thecontext (e.g., it includes the degree of error associated withmeasurement of the particular quantity). All ranges disclosed herein areinclusive of the endpoints, and the endpoints are independentlycombinable with each other.

Although the different non-limiting embodiments have specificillustrated components, the embodiments of this invention are notlimited to those particular combinations. It is possible to use some ofthe components or features from any of the non-limiting embodiments incombination with features or components from any of the othernon-limiting embodiments.

It should be appreciated that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould also be appreciated that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein, however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reason,the appended claims should be studied to determine true scope andcontent.

What is claimed is:
 1. An interface assembly for a gas turbine engine,comprising: an engine case that defines an engine axis, the engine casecomprises an anti-rotation case slot; a full-hoop vane ring around theengine axis, the full-hoop vane ring comprises a forward vane rail witha vane ring forward contact surface and a vane ring anti-rotation tab,the vane ring anti-rotation tab engaged with the anti-rotation caseslot; and a multiple of BOAS segments around the engine axis, each ofthe multiple of BOAS segments comprise a BOAS aft engagement feature anda BOAS aft contact surface, the BOAS aft engagement feature engaged withthe engine case and the anti-rotation case slot, the BOAS aft contactsurface abuts the vane ring forward contact surface, wherein the BOASanti-rotation tab is circumferentially offset from the vane ringanti-rotation tab.
 2. The interface assembly as recited in claim 1,wherein the vane ring forward contact surface loads against the BOASsegment contact surface in response to attachment of a second enginecase to the engine case.
 3. The interface assembly as recited in claim2, wherein the second engine case comprises a turbine exhaust case. 4.The interface assembly as recited in claim 2, wherein the BOAS aftengagement feature of each of the multiple of BOAS segments comprises atleast one BOAS anti-rotation tab.
 5. The interface assembly as recitedin claim 1, further comprising a full hoop seal arranged around theengine axis, the multiple of BOAS segments loaded against the full hoopseal.
 6. The interface assembly as recited in claim 5, wherein the fullhoop seal is a dogbone seal.
 7. The interface assembly as recited inclaim 1, wherein the BOAS aft engagement feature is engaged with theengine case, the BOAS aft engagement feature forms a forward facinghook.
 8. The interface assembly as recited in claim 1, wherein theforward vane rail comprises a groove to receive a seal.
 9. The interfaceassembly as recited in claim 1, wherein each of the multiple of BOASsegments comprises a circumferential feather seal slot to seal betweeneach of the multiple of BOAS segments.
 10. The interface assembly asrecited in claim 1, wherein the engine case comprises a case groove withan anti-rotation case slot that receives the vane ring anti-rotation taband the BOAS anti-rotation tab.
 11. The interface assembly as recited inclaim 10, wherein the BOAS aft engagement feature comprises a rail withthe BOAS anti-rotation tab to receive the vane ring anti-rotation tab.12. The interface assembly as recited in claim 11, wherein the BOAS aftengagement feature is a hooked rail.
 13. The interface assembly asrecited in claim 12, further comprising a BOAS forward engagementfeature received within a groove in the engine case.
 14. A method ofassembling a module for a gas turbine engine, comprising: installing afull-hoop vane ring around an engine axis into a case groove with ananti-rotation slot in an engine case, the full-hoop vane ring comprisesan forward vane rail with a vane ring forward contact surface and a vanering anti-rotation tab received into the anti-rotation slot in theengine case; and installing a multiple of BOAS segments around theengine axis, each of the multiple of BOAS segments comprise a BOAS aftengagement feature, a BOAS aft contact surface, and a BOAS anti-rotationtab, the BOAS anti-rotation tab engaged with the anti-rotation slot inthe engine case such that the BOAS aft contact surface abuts the vanering forward contact surface and the BOAS anti-rotation tab iscircumferentially offset from the vane ring anti-rotation tab.
 15. Themethod as recited in claim 14, further comprising attaching a secondengine case to the engine case to seal the BOAS segment contact surfacewith the vane ring forward contact surface.
 16. The method as recited inclaim 15, further comprising compressing a seal between the full-hoopvane ring and a second multiple of BOAS segments forward of thefull-hoop vane ring.
 17. The method as recited in claim 16, furthercomprising installing the seal within a groove formed in the full-hoopvane ring.